The inscription of images on various surfaces has become increasingly important in recent years for the permanent identification of valuable objects in addition to forming decorative designs on surfaces. For example, for the permanent identification of automobiles, trucks and the like, vehicle VIN Numbers or other identifying indicia are permanently inscribed on the windows of the vehicle at various locations to provide a non-removable identification for the vehicle. Many insurance companies offer a discount from the cost of insuring the vehicle if such permanent indicia are placed on the vehicle. Such indicia, for example a bar code, can also provide an access code for the retrieval of the history of the vehicle, such as for example its previous owner, its maintenance history and the like.
Conventionally, the inscription process is accomplished by mechanical or chemical means. For example, a malleable surface, such as wood, certain precious metals and the like, can be mechanically inscribed using a router or similar tool. These tools can be manually operated by persons possessing relatively high degree of skill or can be robotically controlled to mass produce inscriptions of various kinds on the malleable surface. However, manual operation is slow and not suited to repetitive operations while robotic equipment is expensive and can present a substantial maintenance problem.
In the case of hard surfaces such as glass, chemical etching utilizing a stencil is a common method employed for the inscription of indicia on the surface of the glass. A suitable etchant is placed on the back of the stencil and the etchant contacts the glass surface through the openings in the stencil. The etchant chemically attacks the surface to permanently etch an image corresponding to the stencil openings into the glass surface. Examples of such methods are represented by U.S. Pat. No. 4,585,514 granted Apr. 29, 1986 to L. Joe Scallan and U.S. Pat. No. 4,985,115 granted Jan. 15, 1991 to Thomas DeRossett. Both of these employ chemical etchants to etch an image into the surface of glass.
It is well understood, however, that glass and other inorganic oxide containing materials are relatively chemically resistant. Therefore, the etchant must be of a highly corrosive nature in order to react with the glass surface to form an image. Most of the etchant compounds are hydrogen fluoride based and as such, are highly corrosive and dangerous to use. Also, disposal of such materials can also be a serious problem in view of the potentially harmful environmental affect such materials may have. These materials must be treated as toxic substances and disposed of only at approved sites and transported in an approved manner. Needless to say the disposal of toxic materials is an expensive operation.
As an alternative to the chemical etch, sandblasting can be utilized as a method for etching glass and other similar surfaces. Sandblasting, if not properly carried out, also posses an environmental threat as well as a potential safety hazard to the operators and other personnel in the immediate area of the sandblasting operation. It is necessary to provide adequate protection for the operators of the sandblasting equipment as well as expensive air filtering apparatus to avoid air pollution violations.
Neither chemical etching nor sandblasting readily lend themselves to automation and in most cases, the indicia which can be etched onto the glass surface are limited to non-machine readable numbers. Moreover, poor technique, particularly in the case of chemical etching, can lead to erroneous results due to blurring of the etched image making it difficult to read, especially by machine. It must be noted, particularly in the case of automobile VIN numbers, that accuracy and image quality are of the utmost importance and mistakes require the replacement of the vehicle window or windshield, an expensive procedure.